Scientific instruments such as mass spectrometers often require high or ultra high vacuum conditions in at least the lowest pressure stage, where e.g. detection takes place. Especially in isotope ratio mass spectrometry, deflection mass spectrometers with multiple collectors are advantageous due to their high precision and dynamic range; these multicollector mass spectrometers need large vacuum systems with a plurality of pressure stages. In general, vacuum chambers for these instruments are made from stainless steel, often using prefabricated standard parts such as flanges; different vacuum chambers are interconnected by flanges welded to the wall of respective chamber. The heat introduced during welding may lead to deformation of the work pieces, so that manufacturing precision is limited. Sealing of the connection between a first vacuum chamber and a second vacuum chamber is generally performed by metal seals such as gold or silver wire gasket—which are difficult to use—or copper gaskets (for CF flanges)—which are only available in a limited set of sizes. As a consequence, the cost for manufacturing of the vacuum systems is high, and dimensions are often limited by the available standard components.
UK patent GB 249233 B discloses a vacuum apparatus having a vacuum pump for evacuating two or more volumes, the pump having a number of pressure stages and at least two suction inlets, wherein an outer suction inlet for a first pressure stage is connected to a first volume for evacuation thereof, which first volume spatially surrounds an inner suction inlet for second pressure stage which is connected to a second volume for evacuation thereof, such that the inner suction inlet is an ultra high vacuum inlet and only seals against pressure within the first volume and not against an external pressure, and is separated from the first volume by a metal-to-metal seal that does not cause plastic deformation of the metals of the seal. It is particularly well suited for small ion trap mass spectrometers, where the ion trap is in an ultrahigh vacuum inner volume and other vacuum stages comprising further ion optical elements can be built around the ultra high vacuum volume to facilitate sealing. However, with commercially available multiport pumps such as splitflow turbomolecular pumps, this concept is limited to small instruments.
UK patent application GB 2504329 A describes a sealing arrangement for an ultra high vacuum pump having first and second housing members, the first housing member housing a pumping mechanism, the sealing arrangement being positioned to provide a seal between the first and second housing members, wherein the sealing arrangement comprises inner and outer seals extending around the periphery of the first housing member and a plenum positioned between the inner seal and the outer seal, and wherein pumping means are provided for pumping the plenum to a sub-atmospheric pressure. In a preferred embodiment, the pumping means is provided by parts of the pumping mechanism; this concept aims at manufacturing ultra high vacuum pumps with a cheaper envelope.
Against this background it is a goal of this invention to provide for a cheap and reliable vacuum system for applications requiring high or ultra high vacuum, in particular requiring ultra high vacuum volumes of more than 1000 cm3.